Current transformer



Oct. 1930. F. J. FISCHER CURRENT TRANSFORMER Filed June 5, 1928 2 Sheets-Sheet l [/7 y/v 50/" 55pm ZMW @W 4%;

Oct. 14, 1930. F. J. FISCHER CURRENT TRANSFORMER Filed June 5, 1928 2 Sheets-Sheet 2 Patented Oct. 14, 1930 UNITED STATES PATENT OFFICE FRANZ JOSEPH FISCHER, OF DRESDEN, GERMANY, ASSIGNOB TO KOGH & STEBZEL,

AKTIENGESELLSCHAFT,

OF DBESDEN, GERMANY CURRENT TRANSFORMER Application filed June 6, 1928, Serial No My invention relates to current transformers and more particularly to transformers of the kind in which one of the legs of the shell transformer core and'thesecondary coil are arranged in atransverse passage or tunnel of an insulator, the primary coil being wound on the outside of the tunnel.

It is. an object of my invention to improve a transformer of this general description and to this end instead of an insulator which is open at the bottom I provide an insulator having a closed base. The bottom of the insulator may be a separate cap or cover of insulating material or, preferably, the hottom is made integral with the body of the insulator.

This improvement by which the highvoltage parts of the insulator are surrounded by the body of the transformer in downward direction, that is, toward earth, brings about increased reliability and possibility of providing several improvements with a view to still further increasing the reliability and to simplify and facilitate the manufacture of the insulator.

Firstly, as the cavity of the insulator is electrically insulated throughout, it is no longer necessary to fill it with a liquid or plastic insulating material which not only involves difiiculties as to leakage but may also cause accidents, andevenexpl'osions in case of excessive heating of the apparatus. Instead of a filling of this kind, a granular substance may be provided, for instance a mixture of sand and black lead. This filling is a semi-conductor and therefore permits a very favorable distribution of the static field, fitting the edges and corners of the insulator where there is liability to break down and preventing crowding of the lines of force and relying on the insulator alone for insulating the high-voltage gradient.

Secondly, with a filling of this kind it is not necessary to take special precautions against leakage, such as the cementing of joints, but the packing of the space in which the filling is contained may be effected by less elaborated means such as acking rings or washers of resilient material on which 5u pressure is exerted.

. 282,922, and in Germany August 4, 1927.

The liability of glow discharge at the edges of the metal parts surrounding the insulator on the outside which is brought about by the semi-conductive filling of sand and black lead is counteracted by the very simple expedient of providing an annular flange on the insulator which is preferably fluted on its lower surface and by securing or spraying a thin layer of metal on the base of the insulator for shielding the base statically, which layer extends into the flute.

Thirdly, it is not strictly necessary to provide a metal casin surrounding the base of the insulator, as t e base is closed, and the usual metal casing can be replaced by the thin layer of metal aforesaid. Preferably however the metal casing is provided not as a closure but as a protective cap for the in- SlilatOI and for facilitating its mounting in p ace. 7

In the drawings aflixed to this'specification and forming part thereof a single and a cascade current transformer are illustrated diagrammatically by way of example.

More partciularly,

Fig. 1 is a vertical section of a single transformer,

Fig. 2 is a section taken at right angles to that in Fig. 1, and illustrating a modified packing for the metal casing,

Fig. 3 is a plan view of the insulator, and

Fig. 4 is a section on the line IVIV in Fig. 2,

ig. 5 is a vertical section of a cascade transformer,

Fig. 6 is a section of the upper part of the transformer taken at right angles to the section in Fig. 5, and

Fig. 7 is a section on the line VII-VII in Fig. 6.

Referring first to Figs. 1 to 4, 1 is the body of the insulator which may be made of porcelain or some other suitable material and is here illustrated as having the shape of a square bottle, whic h is closed at the base by a bottom 1 which as shown is integral with its body but, as mentioned, may be a separate cap or cover. 2 is the transverse passage or tunnel referred to, 3 is the core of a shelltype transformer, 3 is the central leg of the core which is inserted in the tunnel 2 with the secondary 4, the primary 5 to which the conductor 5 is connected being wound on the outside of the tunnel. Preferably the clearance between the tunnel 2 and the inner wall of the body 1 is'made so .small that it is just possible to wind the primary 5 on they tunnel.

6 is a layer of metal which is sprayed onto the base 1 or secured thereon by any other suitable means, 7 is an annular flange on the insulator and 6 is a flute on its lower face.

Preferably the layer 6 extends into the flute.

That portion of the shell core 3 which projects on the outside of the insulator, and the base of the insulator are surrounded by a metal casing, 8 being a 'flange'which is cemented to the insulator 1 below the flange 7 as'shown in Fig. 1, 9 is a metal casing which is secured to the flange 8 by any suitable means, for instance, screws, 11 is a resilient insertion between the bottom 1 of the insulator and the-bottom of the casing 9, 12 is a threaded plug in the bottom of the easing, and 13 is a mixture of sand and black lead with which the casing'9 is filled throughthe plug 12, with the transformer held upside down. 13' is a filling, preferably of the same material, in the cavity of the insulator.

Instead of cementing-the flange 8 to the insulator 1, it may be secured by a'rubber ring 10 as shown in Fig. 2, the ringbeing placed on a beveled projection 10 which extends on threesides of the insulator and is engaged by a corresponding beveled face 8' of the flange 8. On the fourth side a circular groove is made in the insulator for the reception of the rubber ring and a corresponding croze 8" is formed on the flange 8.

14 is "a lug closing the insulator at the top throng which the ends of the primary 5 extend and 1 is a packing washer below the plug. Theplug 14 is inserted in a cavity at the top of'the insulator and held in-positionby' an annulus 16 and a rubber ring 15, thrust being exerted on the annulus and the ring by screws 17 extending through the plug 14.

14' is a cap on the plug 14 and 14" is a bracket having suitable binding posts for connecting wires with the ends of the conductor 5 as will appear from Fig. 3.

Referring now to Figs. 5, 6 and 7, these figures illustrate a transformer of the cascade type which is built up by providing two or more superimposed insulators. In the present instance, two insulators 1A and 1B are illustrated, the upper insulator 1A bein designed exactly as the insulator 1 whicfi has been described with reference to Figs. 1 to 4 and its parts have been marked with the same reference numerals as in-that figure. However, the casing 9A is modified in this instance, being open at the bottom for receiving. the neck of the lower insulator IE on. which the shell core 3 is supported. The

flange 8 is cemented to the upper insulator as described and the casing 9 is cemented-to the neck of the lower insulator 1B at 9B.

The bottom of the lower ,insulator 1B is designed similarly to that of the upper insulator 1A, having a transverse passage or tunnel 2 a shell core 3", the middle leg 3 of which with itssecondary i is inserted in the tunnel, .and the primary 5 wound on the outside of the tunnel. 4 are conductors connecting the secondary 4 of the upper insulator with the primary 5" of the lower insulator.

A flange 7A with a flute 6B is formed on the lower insulator 1B and the bottom of the insulatoris provided with a metal layer 6A. 8A is a. flange similar to the flange 8, 9B is a casing similar to the casing 9 described with reference to Figs. 1 to 4, and 13, 13' and 13 are the fillings of the chamber 9B, the lower insulator 1B, and the upper insulator 1A, respectively.

As mentioned, I am not limited to a transformer having two grades but may provide any number of grades with insulators of corresponding design and, preferably, all insulators of a unit are designed and connected as described.

Generally I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled inthe art.

I claim 1. In a pot-shaped current transformer, an insulator having a closed bottom integral with its body, a tunnel extending transversely through said body, a casing surrounding said bottom, and a filler of sand and black lead in said casing.

'2. In a pot-shaped current transformer, an insulator having a closed bottom integral with its body, a tunnel extendingtransversely through said body, static shielding means on said bottom, and a flange surrounding said insulator above said shielding means, said flange being fluted on its lower face and said shielding means extending into said fluted portion.

3. In a pot-shaped current transformer,

' an insulator having a closed bottom integral with its body, a tunnel extending transverse- 1y through said body, static shielding means on said bottom, a flange surrounding said insulator above said shielding means, said flange being fluted on its lower face and said shielding means extending into said fluted portion, and a casing surrounding said bottom below said flange.

4. In a pot-shaped current transformer, an insulator having a closed bottom integral with its body, a tunnel extending transverse- Ill) 1y through said body, and a filling of sand and black lead in said insulator.

5'. In a pot-shaped current transformer, an insulator having a closed bottom integral with its body, a tunnel extending transverse-- pot-shaped insulator having its neck portion and closed bottom portion all in one piece, and a tunnel portion extending transversely through said insulator.

7 A, current transformer comprising -'a pot-shaped insulator having its neck portion and closed bottom portion all in one piece, a tunnel portion extending transversely through said insulator, and a primary winding wound on the outside of said tunnel and totally enclosed by the neck'and bottom portions of said insulator. Y

8. A current transformer comprising a set of superposed pot-shaped insulators, each having its neck portion and closed bottom portion all in one piece, and tunnel portions extending transversely through said insulators the neck portion of each lower insulator being provided with means for receiving tle bottom portion ofthe insulator on top 0 it.

9. A current transformer comprising a. set of superposed pot-shaped insulators, each having its neck portion and closed bottom portion all in one piece, tunnel portions extending transversel through said insulators, the neck portion 0 each lower insulator being provided with means for receiving the bottom portion of the insulator on top of it,

and means for securing said insulators to each other. v

10. A current transformer com rising a pot-shaped insulator having its noel portion and closed bottom portion all in one piece, a tunnel portion extending transversel through said insulator and metallic shield ing means on the outsideof said bottom portion.

11. A current transformer comprising a pot-shaped insulator, having its neck portion and closed bottom portion all in one piece, a tunnel portion extending transversely through said insulator, a casing surrounding said bottom portion and a semi-conductive filler in said casing.

12. A current transformer comprising a pot-shaped insulator, having its neck portion and closed bottom portion all in one piece, a tunnel portion extending transversely through said insulator, a primary winding wound on the outside ofsaid tunnel and totally enclosed by said neck and bottom 7 portions, a transformer core,.a leg of said core lnserted 1n said tunnel portion and a secondary winding wound on said leg within" said tunnel.

13. A current transformer comprising a pot-shaped insulator having its neck portion and closed bottom portion all in one piece, a tunnel portion extending transversely through said insulator, a metal casing surrounding said bottom, and a resilient pack-.

ing inserted between said insulator and said casing.

In testimony whereof I ailix my signature.

' FRANZ JOSEPH FISCHER. 

